The present invention relates to an optical fiber to be optically coupled with a device for optical communication.
In an optical communication system, an optical fiber is coupled to an optical communication device, such as an optical network unit (ONU). The optical communication device generally includes a laser diode for emitting a laser beam modulated in accordance with data to be transferred and a converging lens for converging the laser beam on an entrance face of the optical fiber. In order to efficiently transmit the laser beam through the optical fiber, the laser beam should be converged on the center of the core of the optical fiber's entrance face. This requires very precise positioning of the laser diode and the converging lens against the optical fiber since the core of the optical fiber has a diameter of only a few micrometers (e.g. about 10 μm).
Conventionally, positioning of the laser diode and/or the converging lens against the optical fiber is carried out by detecting the light amount of the laser beam passed through the optical fiber. The optical fiber is moved relative to the laser beam until the detected light amount exceeds a predetermined level. When the detected light amount exceeds the predetermined level, it is determined that the laser beam emitted from the laser diode impinges on the center of the optical fiber's core.
In the conventional method mentioned above, it is necessary to first visually adjust the incident position of the laser beam to the core of the optical fiber's entrance face so that at least a part of the laser beam passes through the optical fiber. However, since it is difficult to visually distinguish the core from the cladding, the position of the laser diode relative to the optical fiber must be first adjusted by trial and error until the laser beam enters the core of the optical fiber and can be detected on the other end (exit end) of the optical fiber. This process is troublesome and time consuming.
Further, after the positioning of the laser diode and the converging lens is achieved, the positions thereof relative to the optical fiber may change with age and cause poor optical coupling between the laser diode and the optical fiber. However, after the optical fiber is installed in an optical communication system, re-adjustment of the optical coupling between the optical fiber and the laser diode cannot be carried out easily by the above-mentioned conventional method since the exit end of the optical fiber is connected to another device and does not allow measurement of the power of the laser beam emerging therefrom.
Therefore, there is a need for an optical fiber that facilitates an adjustment of a position of a light beam incident on an entrance face of the optical fiber.
There is also a need for an optical fiber of which optical coupling with a device for optical communication can be re-adjusted with ease even after the optical fiber is installed in an optical communication system.